1. Field of the Invention
The present invention relates to a device which keeps a visible image, corresponding to an optical image obtained through a photographing lens, on a recording medium and which can read the visible image from the recording medium.
2. Description of the Related Art
Conventionally, silver halide photographic material is generally used as a material for recording an optical image. Silver halide photographic material has high optical sensitivity and high resolution, and the economical efficiency thereof is excellent. However, silver halide photographic material has drawbacks in that not only is the developing process cumbersome but also a visible image cannot be obtained at the same time that the photograph is taken. A dry-type developing method has been developed to simplify the developing process. However, simultaneous development in which a visible image is obtained upon photography is impossible in the dry-type developing method.
On the other hand, as non-silver-halide photographic materials, there are known electrophotographic materials, diazo type photographic materials, free-radical photographic materials and so on. In these materials, however, there is no material which has advantageous characteristics like silver halide photographic material, while being able to simultaneously develop and keep a visible image. Note that, electrophotographic materials have been used mainly in copying machines, since they can perform dry-type development and can simultaneously develop an electrostatic latent image, which is obtained by exposure, using toner.
In such electrophotographic materials, recently, a photographic material has been developed in which a recording medium made of the photographic material is electronically and directly developed similarly to a silver halide photographic material, so that the developed visible image can be immediately seen or recorded. Such a recording medium in which a visible image is electronically developed is referred to as an electro-developing recording medium in this specification.
Japanese Unexamined Patent Publication No. 5-2280, for example, discloses a recording medium which is a combination of an electrostatic information recording medium and an electric charge keeping medium, the electrostatic information recording medium having a photoconducting layer and an inorganic oxide material layer, and the electric charge keeping medium having a liquid crystal display. In this structure, when the electrostatic information recording medium is exposed while an electric voltage is applied to the electrostatic information recording medium and the electric charge keeping medium, electric charge in accordance with the amount of incident light is generated in the electrostatic information recording medium. Since the intensity of electric field applied to the liquid crystal display facing the electrostatic information recording medium is varied in accordance with the generated electric charge, an image corresponding to the amount of light distribution is indicated or developed on the liquid crystal display.
Japanese Unexamined Patent Publication No. 5-150251 discloses a dispersion type liquid crystal display in which an image indicated on the liquid crystal display is kept even if the electric field applied to the liquid crystal display is removed.
On the other hand, there is known a camera by which an image obtained by a photographing lens is formed on a plane in space as an aerial image, which is then formed onto an optical sensor through a scanner optical system to record the image on a recording medium.
The camera may be designed in such a manner that the electro-developing recording medium can be mounted, and the image developed by the electro-developing recording medium, or the aerial image can be recorded. However, since the electro-developing recording medium has sheets of glass for confining liquid crystal elements therein, the image position formed by the photographing optical system is changed depending upon whether or not the electro-developing recording medium is present, and thus the focusing position of the scanner optical system changes so that an in-focus image can not be formed on an optical sensor.
Further, when the image developed on the liquid crystal display is sensed by an optical sensor such as a line sensor, a light source is placed on one side of the liquid crystal display and the line sensor is placed on the other side of the liquid crystal display, and thus, a light beam, which is outputted by the light source and passes through the liquid crystal display, is read by the scanner optical system and the line sensor. Namely, the light source is provided on the optical axis of the scanner optical system. However, if the light source is positioned close to the electro-developing recording medium in a photographing operation, an eclipse (or vignetting) occurs on the recording medium, and thus the amount of light exposed onto the recording medium may be insufficient.
Furthermore, in such a structure, when the light source is located in a portion between the photographing optical system and the electro-developing recording medium, the back focus of the photographing optical system cannot be sufficiently short, since the space that the portion occupies must be large enough to dispose or accommodate the light source so that the degree of freedom of the design of the photographing optical system is low.